Induction system for small watercraft

ABSTRACT

An induction system for a 4-cycle engine of a small watercraft includes an improved construction that insulates the fuel injectors from engine-produced vibration and heat. The air induction system includes an air intake box defining the plenum chamber. The air intake box is supported from the engine by one or more stays. An insulating grommet is positioned between the air intake box and the stays. The air induction system also includes one or more throttle bodies within the plenum chamber which are connected to intake pipes external of the plenum chamber. The throttle bodies each support a fuel injector. Insulating sleeves are positioned between the throttle bodies and the intake pipes. Insulating rings are positioned between the throttle bodies and the air intake box.

PRIORITY INFORMATION

[0001] This invention is based on and claims priority to Japanese PatentApplications No. 200-205618, filed Jul. 6, 2000, the entire contents ofwhich are hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to an engine for a watercraft, andparticularly to an improved air induction system of an engine for awatercraft.

[0004] 2. Description of the Related Art

[0005] Personal watercrafts have become very popular in recent years.This type of watercraft is quite sporting in nature and carries one ormore riders. A relatively small hull of the personal watercraft commonlydefines a rider's area above an engine compartment. An internalcombustion engine powers a jet propulsion unit which propels thewatercraft. The engine lies within the engine compartment in front of atunnel formed on an underside of the hull. The jet propulsion unit,which includes an impeller, is placed within the tunnel. The impellerhas an impeller shaft driven by the engine. The impeller shaft usuallyextends between the engine and the jet propulsion device through abulkhead of the hull tunnel.

[0006] The engine includes an air induction system for delivering airinto one or more combustion chambers. The engine also includes a fueldelivery system for introducing fuel into the one or more combustionchambers. In order to reduce emissions, the fuel delivery system oftenincludes at least one electronically controlled fuel injector associatedwith the combustion chambers. An electronically controlled fuel injectoris capable of more precise metering of fuel delivery than mechanicalsystems, such as carburetors.

[0007] Typically, the fuel injector is mounted to a component of the airinduction system which, in turn, is mounted to the engine. Often, thefuel injector is mounted to a throttle body of the fuel delivery system.This arrangement results in vibration and heat produced by the engine tobe transferred through the throttle body to the fuel injector. Theelectronic components of the fuel injector may be negatively affected byexposure to vibration and/or heat, which results in lower performance,decreased life and a higher rate of premature failure.

SUMMARY OF THE INVENTION

[0008] According to one aspect a preferred embodiment, a watercraftincludes a hull defining an engine compartment. An internal combustionengine is positioned within the engine compartment. The engine includesan engine body which defines a combustion chamber. An air inductionsystem is provided which is configured to guide air into the combustionchamber and includes an intake air chamber. An electronic component issupported within the intake chamber. A first insulating member connectsthe intake air chamber to the engine body.

[0009] According to another aspect of the preferred embodiment a marineduty engine includes an engine body which defines a combustion chamber.An air induction system is configured to guide air into the combustionchamber and includes an intake air chamber and a throttle body. Anelectrical component is disposed in the air chamber. A first insulatingmember connects air intake chamber to the engine.

[0010] According to another aspect the preferred embodiment, awatercraft includes a hull defining an engine compartment. An internalcombustion engine is positioned within the engine compartment. Theengine includes an engine body which defines a combustion chamber. Anair induction system is provided which is configured to guide air intothe combustion chamber and includes a throttle body. A fuel deliverysystem is provided which is configured to deliver fuel to the combustionchamber and includes a fuel injector. The fuel injector is supported bythe throttle body. A first insulating member connects the throttle bodyto the engine.

[0011] In accordance with another aspect of the preferred embodiment, asmall watercraft includes a hull defining an engine compartment. Aninternal combustion engine is positioned within the engine compartment.The engine includes an engine body which defines a combustion chamber.An air induction system is configured to guide air into the combustionchamber and includes a throttle body. A fuel delivery system is providedwhich is configured to deliver fuel to the combustion chamber andincludes a fuel injector. The fuel injector is supported by the throttlebody. Means for inhibiting engine produced vibrations from beingtransferred to the fuel injector is provided.

[0012] A still further aspect of a preferred embodiment involves a smallwatercraft including a hull defining an engine compartment. An internalcombustion engine is positioned within the engine compartment. Theengine includes an engine body which defines a combustion chamber. Anair induction system is provided which is configured to guide air intothe combustion chamber and includes a throttle body. A fuel deliverysystem is provided which is configured to deliver fuel to the combustionchamber and includes a fuel injector. The fuel injector is supported bythe throttle body. Means for inhibiting engine produced vibrations frombeing transferred to the fuel injector is provided.

[0013] Further aspects, features and advantages of this invention willbecome apparent from the detailed description of the preferredembodiments which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects and advantages of the presentinvention will now be described with reference to the drawings ofpreferred embodiments which are intended to illustrate and not to limitthe invention. The drawings comprise 8 figures.

[0015]FIG. 1 is a side elevational view of a personal watercraft of thetype powered by an engine configured in accordance with a preferredembodiment of the present invention. Several of the internal componentsof the watercraft (e.g., the engine) are illustrated in phantom.

[0016]FIG. 2 is a top plan view of the watercraft shown in FIG. 1.

[0017]FIG. 3 is a schematic and partial cross-sectional rear view of thewatercraft and the engine. A profile of a hull of the watercraft isshown schematically. The engine including an air intake box and anopening of an engine compartment of the hull are illustrated partiallyin section.

[0018]FIG. 4 is a front, top, and right side perspective view of theengine shown in FIG. 3.

[0019]FIG. 5 is a front, top, and left side perspective view of theengine shown in FIG. 3.

[0020]FIG. 6 is a top plan view of the intake box. An upper chambermember is detached in this figure.

[0021]FIG. 7 is an enlarged cross-sectional view of a portion of theintake box shown in FIG. 3.

[0022]FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG.6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] With reference to FIGS. 1 to 8, an overall configuration of apersonal watercraft 10 is described below. An arrow F, present inseveral of the figures, indicates a forward direction of the watercraft10.

[0024] The watercraft 10 employs an internal combustion engine 12configured in accordance with a preferred embodiment of the presentinvention. The described engine configuration has particular utilitywith the personal watercraft, and thus, is described in the context ofthe personal watercraft 10. The engine configuration, however, can beapplied to other types of watercrafts as well, such as, for example,small jet boats.

[0025] The personal watercraft 10 includes a hull 14 formed with a lowerhull section 16 and an upper hull section or deck 18. Both the hullsections 16, 18 are made of, for example, a molded fiberglass reinforcedresin or a sheet molding compound. The lower hull section 16 and theupper hull section 18 are coupled together to define an internal cavity20 (FIG. 3). A gunnel 22 defines an intersection of both the hullsections 16, 18.

[0026] With reference to FIGS. 1 through 3, the hull 14 defines a centerplane CP that extends generally vertically from bow to stern. Along thecenter plane CP, the upper hull section 18 includes a hatch cover 24, acontrol mast 26 and a seat 28 arranged from fore to aft.

[0027] In the illustrated embodiment, a bow portion 30 of the upper hullsection 18 slopes upwardly and an opening (not shown) is providedthrough which the rider can access the internal cavity 20. The hatchcover 24 is detachably affixed (e.g., hinged) to the bow portion 30 soas to cover the opening.

[0028] The control mast 26 extends upwardly to support a handle bar 32.The handle bar 32 is provided primarily for controlling the direction inwhich the water jet propels the watercraft 10. Grips are formed at bothends of the bar 32 so that the rider can hold them for that purpose. Thehandle bar 32 also carries other control units such as, for example, athrottle lever 34 that is used for control of running conditions of theengine 12.

[0029] The seat 28 extends along the center plane CP to the rear of thebow portion 30. The seat 28 also generally defines a rider's area. Theseat 28 has a saddle shape and hence a rider can sit on the seat 28 in astraddle-type fashion. Foot areas 36 are defined on both sides of theseat 28 on the top surface of the upper hull section 18. The foot areas36 are formed generally flat.

[0030] A cushion supported by the upper hull section 18, at least inprincipal part, forms the seat 28. The seat 28 is detachably attached tothe upper hull section 18. An access opening 38 is defined under theseat 28 through which the rider can also access the internal cavity 20.That is, the seat 28 usually closes the access opening 38. In theillustrated embodiment, the upper hull section 18 also defines a storagebox 40 under the seat 28.

[0031] A fuel tank 42 is disposed in the cavity 20 under the bow portion30 of the upper hull section 18. The fuel tank 42 is coupled with a fuelinlet port positioned at a top surface of the upper hull section 18through a duct (not shown). A closure cap 44 closes the fuel inlet port.Optionally, the cap 44 can be positioned under the hatch cover 24.

[0032] The engine 12 is disposed in an engine compartment defined in thecavity 20. The engine compartment preferably is located under the seat28, but other locations are also possible (e.g., beneath the controlmast 26 or in the bow). The rider thus can access the engine 12 in theillustrated embodiment through the access opening 38 by detaching theseat 28.

[0033] A pair of air ducts or ventilation ducts 46 are provided on bothsides of the bow portion 30 so that the ambient air can enter theinternal cavity 20 therethrough. Optionally, the watercraft 10 can alsoinclude additional air ducts (not shown) which allow air to enter andexit the engine internal cavity 20 through a rear area thereof. Exceptfor the air ducts, the engine compartment 20 is substantially sealed soas to protect the engine 12 and other components from water.

[0034] A jet pump unit 48 propels the watercraft 30. The jet pump unit48 is mounted at least partially in a tunnel 50 formed on the undersideof the lower hull section 36 which is preferably isolated from theengine compartment by a bulkhead (not shown). The tunnel 50 has adownward facing inlet port (not shown) opening toward the body of water.A jet pump housing 52 is disposed within a portion of the tunnel 50 andcommunicates with the inlet port. An impeller (not shown) is supportedwithin the housing 52.

[0035] An impeller shaft 54 extends forwardly from the impeller and iscoupled to a crankshaft 56 of the engine 12 by a coupling member 58. Thecrankshaft 56 of the engine 12 thus drives the impeller shaft 54.

[0036] The rear end of the housing 52 defines a discharge nozzle 59. Asteering nozzle 60 is affixed to the discharge nozzle 59 for pivotalmovement about a steering axis which extends generally vertically. Thesteering nozzle 60 is connected to the handle bar 32 by a cable so thatthe rider can pivot the nozzle 60.

[0037] As the engine 12 drives the impeller shaft 54 and hence rotatesthe impeller, water is drawn from the surrounding body of water throughthe inlet port (not shown). The pressure generated in the housing 52 bythe impeller produces a jet of water that is discharged through thesteering nozzle 60 which propels the watercraft 10. The rider can movethe steering nozzle 60 with the handle bar 32 so as to turn thewatercraft 30 in either direction.

[0038] The engine 12 operates on a four-stroke cycle combustionprinciple. With reference to FIG. 3, the engine 12 includes a cylinderblock 62. The cylinder block 62 defines four cylinder bores 64 which arespaced from each other in a fore to aft direction along the center planeCP. The engine 12 thus is an L4 (in-line four cylinder) type. Theillustrated engine, however, merely exemplifies one type of engine onwhich various aspects and features of the present invention can be used.Engines having other number of cylinders, having other cylinderarrangements, other cylinder orientations (e.g., upright cylinder banks,V-type, and W-type) and operating on other combustion principles (e.g.,crankcase compression two-stroke, diesel, and rotary) are allpracticable.

[0039] Each cylinder bore 64 has a center axis CA that is slanted orinclined at an angle from the center plane CP so that the engine 12 canbe shorter in height. All the center axes CA in the illustratedembodiment are inclined at the same angle.

[0040] Pistons 66 reciprocate within the cylinder bores 64. A cylinderhead member 68 is affixed to the upper end of the cylinder block 62 toclose respective upper ends of the cylinder bores 64 and to definecombustion chambers 70 with cylinder bores and the pistons 66.

[0041] A crankcase member 72 is affixed to the lower end of the cylinderblock 62 to close the respective lower ends of the cylinder bores 64 andto define a crankcase chamber 74. The crankshaft 56 is rotatablyconnected to the pistons 66 through connecting rods 76 and is journaledwith the crankcase member 72. That is, the connecting rods 76 arerotatably coupled with the pistons 66 and with the crankshaft 56.

[0042] The cylinder block 62, the cylinder head member 68, and thecrankcase member 72 together define an engine body 78. The engine body78 preferably is made of an aluminum based alloy.

[0043] In the illustrated embodiment, the engine body 78 is oriented inthe engine compartment 20 so as to position the crankshaft 56 generallyparallel to the central plane CP and to extend generally in thelongitudinal direction. Other orientations of the engine body, ofcourse, are also possible (e.g., with a transverse or verticalcrankshaft).

[0044] Engine mounts 80 extend from both sides of the engine body 78.The engine mounts 80 preferably include resilient portions made of, forexample, a rubber material. The engine 12 preferably is mounted on thelower hull section 16, specifically, a hull liner, by the engine mounts80 so that vibrations from the engine 12 are attenuated.

[0045] The engine 12 preferably includes an air induction system tointroduce air to the combustion chambers 70. In the illustratedembodiment, the air induction system includes at least four air intakeports 82 defined in the cylinder head member 68, i.e., one for eachcylinder bore 64. The intake ports 82 communicate with the associatedcombustion chambers 70. Intake valves 84 are provided to selectivelyconnect and disconnect the intake ports 82 with the combustion chambers70. That is, the intake valves 84 selectively open and close the intakeports 82.

[0046] The air induction system also includes an air intake box 86,which defines a plenum chamber 88 within, for smoothing intake air andacting as an intake silencer. The intake box 86 in the illustratedembodiment, has a generally rectangular shape. Other shapes of theintake box of course are possible, but it is desired to make the plenumchamber as large as possible within the space provided in the enginecompartment. In the illustrated embodiment, a space is defined betweenthe top of the engine 12 and the bottom of the seat 28 due to theinclined orientation of the engine 12. The rectangular shape of theintake box 86 conforms to this space.

[0047] With reference to FIGS. 3 and 7, the intake box 86 comprises anupper chamber member 90 and a lower chamber member 92. The upper andlower chamber members 90, 92 preferably are made of plastic or syntheticresin, although they can be made of metal or other material.Additionally, the intake box 86 can be formed by a different number ofmembers and/or can have a different assembly orientation (e.g.,side-by-side).

[0048] With reference to FIG. 3, the lower chamber member 92 preferablyis coupled with the engine body 78. In the illustrated embodiment,several stays 94 extend upwardly from the engine body 78 and a flangeportion 96 of the lower chamber member 92 extends generallyhorizontally.

[0049] Several fastening members, for example, bolts 98, connect theflange portion 96 to respective top surfaces of the stays 94. The upperchamber member 90 has a flange portion 100 (FIG. 1) that abuts on theflange portion 96 of the lower member 92. Several coupling or fasteningmembers 102, which are generally configured as a shape of the letter “C”in section, preferably engage both the flange portions 96, 84 so as tocouple the upper chamber member 90 with the lower chamber member 92. Theintake box 86 thus is disposed in a space defined between the enginebody 78 and the seat 28, i.e., the rider's area of the hull 34, so thatthe air intake box 86 defines a relatively large volume plenum chamber88 therein.

[0050] With reference to FIG. 3, 6 and 8, the lower chamber member 92defines an inlet opening 104 and, preferably, four outlet apertures 106.Four throttle bodies 108 extend through the apertures 106 and preferablyare fixed to the lower chamber member 92. Respective bottom ends of thethrottle bodies 108 are coupled with the associated intake ports 82.Preferably, as illustrated in FIG. 3, the position at which theapertures 106 are sealed to the throttle bodies 108 is spaced from theoutlet of “bottom” ends of the throttle bodies 108. Thus, the lowermember 92 is spaced from the engine 12, thereby attenuating transfer ofheat from the engine body 78 into the intake box 86.

[0051] With reference to FIG. 3, the throttle bodies 108 slant towardthe port side away from the center axis CA of the cylinder bores 64. Asleeve 110, described in greater detail below, extends between the lowerchamber member 92 and the cylinder head member 68 so as to generallysurround a portion of the throttle bodies 108. Respective top ends ofthe throttle bodies 108, in turn, open upwardly within the plenumchamber 88. Air in the plenum chamber 88 thus is drawn to the combustionchambers 70 through the throttle bodies 108 and the intake ports 82 whennegative pressure is generated in the combustion chambers 70. Thenegative pressure is generated when the pistons 66 move toward thebottom dead center from the top dead center.

[0052] With reference to FIGS. 6 and 8, each throttle body 108 includesa throttle valve 112. A throttle valve shaft 114, journaled for pivotalmovement, links the throttle valves 112. Pivotal movement of thethrottle valve shaft 114 is controlled by the throttle lever 58 on thehandle bar 56 through a control cable that is connected to the throttlevalve shaft 114. The rider thus can control opening amount of thethrottle valves 112 by operating the throttle lever 56 so as to obtainvarious running conditions of the engine 12 that the rider desires. Thatis, an amount of air passing through the throttle bodies 108 iscontrolled by this mechanism and delivered to the respective combustionchambers 70.

[0053] With reference to FIG. 3, air is introduced into the plenumchamber 88 through the air inlet port 104. In the illustratedembodiment, a filter assembly 116 surrounds the inlet port 104. Thefilter assembly 116 comprises an upper plate 118, a lower plate 120 anda filter element 122 interposed between the upper and lower plates 118,120. Preferably, the filter element 122 comprises oil resistant andwater-repellant elements.

[0054] The lower plate 120 includes a duct 124 which extends inwardlytoward the plenum chamber 88. The duct 124 is positioned generally abovethe cylinder head member 68. An upper end of the duct 124 slants so asto face an inner wall portion of the intake box 86 positioned oppositethe throttle bodies 108. In the illustrated embodiment, the upper oroutlet ends of the ducts 124 define a high point proximate to the outletapertures 106 and a low point distal from the apertures 106. This isadvantageous because water or water mist, if any, is likely to movetoward this inner wall portion rather than toward the throttle bodies108. If, however, a smooth flow of air is desired more than the waterinhibition, the upper end of the duct 124 can slant toward the throttlebodies 108 as indicated by the phantom line 124 a of FIG. 3. Optionally,the upper ends of some of the ducts 124 can slant away from the throttlebodies 108 and the rest can slant toward the throttle bodies 108.

[0055] In the illustrated embodiment, a guide member 126 is affixed tothe lower plate 120 immediately below the duct 124. The guide member 126defines a recess 128 that is associated with duct 124. The recess 128opens toward the starboard side. The air in the cavity 20 of the enginecompartment thus is drawn into the plenum chamber 88 along the recess128 of the guide member 126 and then through the duct 124.

[0056] The filter assembly 116, including the lower plate 120, has agenerally rectangular shape in plan view. The filter element 122 extendsalong a periphery of the rectangular shape so as to define a gap betweena peripheral edge of the filter element 122 and an inner wall of the airbox 86. The duct 124 opens to an interior volume 130 defined by thefilter element 122. The air in this volume 130 thus cannot reach thethrottle bodies 108 without passing through the filter element 122.Foreign substances in the air are removed by the filter element 122accordingly.

[0057] Because the air inlet openings 104 are formed at the bottom ofthe intake box 86, water and/or other foreign substances are unlikely toenter the plenum chamber 88. Additionally, the filter element 106further prevents water and foreign particles from entering the throttlebodies 108. In addition, part of the openings 104 are defined as theducts 106 extending into the plenum chamber 88. Thus, a desirable lengthfor efficient silencing of intake noise can be accommodated within theplenum chamber 90.

[0058] The engine 12 also includes a fuel supply system as illustratedin FIGS. 1, 3, 6 and 8. The fuel supply system includes the fuel tank 42(FIG. 1) and fuel injectors 132 that are affixed to a fuel rail 134 andare mounted on the throttle bodies 108. The fuel rail 134 extendsgenerally horizontally in the longitudinal direction. A fuel inlet port136 is defined at a forward portion of the lower chamber member 92 sothat the fuel rail 134 is coupled with an external fuel passage. Becausethe throttle bodies 108 are disposed within the plenum chamber 88, thefuel injectors 132 are also desirably positioned within the plenumchamber 88. However, other types of fuel injectors can be used which arenot mounted in the intake box 86, such as, for example, but withoutlimitation, direct fuel injectors and induction passage fuel injectorsconnected to the scavenge passages of two-cycle engines. Each fuelinjector 132 has an injection nozzle directed toward the intake port 82associated with each fuel injector 132.

[0059] Sprayed fuel is delivered to the combustion chambers 70 with theair when the intake ports 82 are opened to the combustion chambers 70 bythe intake valves 84. The air and the fuel are mixed together to formair/fuel charges which are then combusted in the combustion chambers 70.

[0060] With reference to FIGS. 3-5, the engine 12 further includes anexhaust system 138 to discharge burnt charges, i.e., exhaust gases, fromthe combustion chambers 70. In the illustrated embodiment, withreference to FIG. 3, the exhaust system 138 includes a plurality ofexhaust ports 140, at least one for each combustion chamber 70. Theexhaust ports 140 are defined in the cylinder head member 68 andcommunicate with the associated combustion chambers 70. Exhaust valves142 are provided to selectively connect and disconnect the exhaust ports140 with the combustion chambers 70. That is, the exhaust valves 142selectively open and close the exhaust ports 140.

[0061] The exhaust system includes an exhaust manifold 144. In apresently preferred embodiment, the manifold 144 comprises a firstmanifold 146 and a second manifold 148 (FIG. 4) coupled with the exhaustports 140 to receive exhaust gases from the respective ports 140. Thefirst manifold 146 is connected to two of the exhaust ports 140 and thesecond manifold 148 is connected with the other two exhaust ports 140.In a presently preferred embodiment, the first and second manifolds 146,148 are configured to nest with each other.

[0062] Respective downstream ends of the first and second exhaustmanifolds 146, 148 are coupled with a first unitary exhaust conduit 150.As seen, for example, in FIGS. 5 and 6, the first unitary conduit 150 isfurther coupled with a second unitary exhaust conduit 152. The secondunitary conduit 152 is then coupled with an exhaust pipe 154 on the rearside of the engine body 78.

[0063] With reference to FIG. 5, the exhaust pipe 154 extends along aside surface of the engine body 78 on the port side. The exhaust pipe154 is then connected to a water-lock 156 at a forward surface of thewater-lock 156. With reference to FIG. 2, a discharge pipe 158 extendsfrom a top surface of the water-lock 156 and transversely across thecenter plane CP. The discharge pipe 158 then extends rearwardly andopens at a stem of the lower hull section 36 in a submerged position.The water-lock 156 inhibits the water in the discharge pipe 158 fromentering the exhaust pipe 154.

[0064] With reference to FIG. 4, the engine 12 preferably includes asecondary air supply system 160 that supplies air from the air inductionsystem to the exhaust system 138. More specifically, for example, hydrocarbon (HC) and carbon monoxide (CO) components of the exhaust gases canbe removed by an oxidation reaction with oxygen (O₂) that is supplied tothe exhaust system 138 from the air induction system.

[0065] With reference to FIG. 3, the engine 12 has a valve cam mechanismfor actuating the intake and exhaust valves 84, 142. In the illustratedembodiment, a double overhead camshaft drive is employed. That is, anintake camshaft 162 actuates the intake valves 84 and an exhaustcamshaft 164 separately actuates the exhaust valves 142. The intakecamshaft 162 extends generally horizontally over the intake valves 84from fore to aft generally parallel to the center plane CP, and theexhaust camshaft 164 extends generally horizontally over the exhaustvalves 142 from fore to aft also generally parallel to the center planeCP.

[0066] Both the intake and exhaust camshafts 162, 164 are journaled bythe cylinder head member 68 with a plurality of camshaft caps. Thecamshaft caps holding the camshafts 162, 164 are affixed to the cylinderhead member 68. A cylinder head cover member 166 extends over thecamshafts 162, 164 and the camshaft caps, and is affixed to the cylinderhead member 68 to define a camshaft chamber. The stays 94 and thesecondary air supply device 142 are preferably affixed to the cylinderhead cover member 166. Additionally, the air supply device 142 isdesirably disposed between the intake air box 86 and the engine body 78.

[0067] The intake camshaft 162 has cam lobes each associated with arespective intake valves 84, and the exhaust camshaft 164 also has camlobes associated with respective exhaust valves 142. The intake andexhaust valves 84, 142 normally close the intake and exhaust ports 82,140 by a biasing force of springs. When the intake and exhaust camshafts162, 164 rotate, the cam lobes push the respective valves 84, 142 toopen the respective ports 82, 142 by overcoming the biasing force of thespring. The air thus can enter the combustion chambers 70 when theintake valves 84 open. In the same manner, the exhaust gases can moveout from the combustion chambers 70 when the exhaust valves 142 open.

[0068] The crankshaft 56 preferably drives the intake and exhaustcamshafts 162, 164. The respective camshafts 162, 164 have drivensprockets affixed to ends thereof. The crankshaft 56 also has a drivesprocket. Each driven sprocket has a diameter which is twice as large asa diameter of the drive sprocket. Preferably, a timing chain or belt iswound around the drive and driven sprockets. When the crankshaft 56rotates, the drive sprocket drives the driven sprockets via the timingchain, and thus the intake and exhaust camshafts 162, 164 also rotate.The rotational speed of the camshafts 150, 238 are reduced to half asthe rotational speed of the crankshaft 56 because of the differences indiameters of the drive and driven sprockets.

[0069] Ambient air enters the internal cavity 20 defined in the hull 34through the air ducts 46. The air is then introduced into the plenumchamber 88 defined by the intake box 86 through the air inlet ports 98and drawn into the throttle bodies 108. The majority of the air in theplenum chamber 88 is supplied to the combustion chambers 70. Thethrottle valves 112 in the throttle bodies 108 regulate an amount of theair passing to the combustion chambers 70. The opening angles of thethrottle valves 112 are controlled by the rider with the throttle lever58 and thus controls the airflow across the valves. The air hence flowsinto the combustion chambers 70 when the intake valves 84 open. At thesame time, the fuel injectors 132 spray fuel into the intake ports 82under the control of ECU. Air/fuel charges are thus formed and deliveredto the combustion chambers 70.

[0070] The air/fuel charges are fired by the spark plugs 216 under thecontrol of the ECU. The burnt charges, i.e., exhaust gases, aredischarged to the body of water surrounding the watercraft 30 throughthe exhaust system 138. A relatively small amount of the air in theplenum chamber 88 is supplied to the exhaust system 138 through thesecondary air supply system 160 so as to aid in further combustion ofany unburnt fuel remaining in the exhaust gases.

[0071] The combustion of the air/fuel charges causes the pistons 66reciprocate and thus causes the crankshaft 56 to rotate. The crankshaft56 drives the impeller shaft 54 and the impeller rotates in the hulltunnel 50. Water is thus drawn into the tunnel 50 through the inlet port76 and then is discharged rearward through the steering nozzle 60. Therider steers the nozzle 60 by the steering handle bar 56. The watercraft30 thus moves as the rider desires.

[0072] Primarily with reference to FIGS. 6 through 8, the air inductionsystem 138, and specifically the throttle body 108 mounting arrangementis described in greater detail below.

[0073] With reference to FIG. 6, the lower chamber member 92 of the airintake box 86 is illustrated with the upper chamber member 90 removed.The lower chamber member 92 includes a pair of brackets 168, eachincluding a through hole 170, for connecting the air intake box 86 tothe stays 94 (FIG. 3).

[0074] With reference to FIG. 7, a mounting arrangement of a singlejunction between the stay 94 and the air intake box 86 is illustrated.Preferably, each mounting junction between each stay 94 and the airintake box 86 is constructed in accordance with the arrangementillustrated in FIG. 7. As described in relation to FIG. 3, the airintake box 86 is supported by one or more stays 94 extending between theengine 12 and the air intake box 86. A bolt 98 and nut 99 secure the airintake box 86 to the stay 94.

[0075] An insulating grommet 172 is positioned concentrically within thethrough hole 170 of the air intake box 86. The grommet 172 preferablyincludes a substantially cylindrical shaped central portion 174 and aflange portion 176 of larger diameter on each end. Preferably, thecentral portion 174 nests within the through hole 170 with one of theflange portions 176 engaging the upper surface of the bracket 168 andone of the flange portions engaging the lower surface of the bracket168. Preferably, the grommet 172 is constructed from a material whichinhibits the transfer of vibration and heat, such as an elastomeric orrubber material, for example.

[0076] The grommet 172 additionally includes a central aperture 178passing axially therethrough. A collar 180 having a flange portion 182at one end is positioned within the central aperture 178 of the grommet172. A washer 184 is positioned at the opposite end from the flangeportion 182 of the collar 180. The flange portion 182 of the collar 180preferably is supported by a transversely extending tab 186 of the stay94. The bolt 98 is passed through the washer 184, collar 180 and stay 94and is secured in place by the nut 99. Thus, the grommet 172 ispositioned intermediate the air intake box 86 and the stay 94 to inhibitengine vibration and/or heat, which is transferred to the stay 94, frombeing passed to the air intake box 86.

[0077] With reference to FIG. 8, a mounting arrangement of the throttlebody 108 is illustrated. FIG. 8 is a cross section of a throttle body108 taken along line 8-8 of FIG. 6. Although only one throttle body 108is illustrated in FIG. 8, preferably the remaining throttle bodies 108are of a similar or identical construction.

[0078] An intake pipe 188 defines an intake runner 190 of the engine 12.The intake runner 190 communicates with the intake port 82 (FIG. 3). Thethrottle body 108 is connected to the intake pipe 188 by the sleeve 110,described in greater detail below. The throttle body 108 defines anaperture for supporting the fuel injector 132 in a position tocommunicate with the intake runner 190.

[0079] The insulating sleeve 110 is secured to the intake pipe 188 by ahose clamp 194. The end of the sleeve 110 opposite the intake pipe 188defines an annular recess 196 for receiving a collar 198. The collar 198may be held by the resilient nature of the sleeve 110 material. However,the collar 198 may also be secured to the sleeve 110 by an adhesive.Alternatively, the sleeve 110 may be injection molded around the collar198 during manufacturing. Other suitable connection methods may also beused.

[0080] The sleeve 110 and collar 198 assembly extends through theopening 106 of the air intake box 86. A flange portion 200 of the collar198 cooperates with a flange portion 202 of the throttle body 108 tosecure a portion of the air intake box 86 therebetween. A bolt 204secures the throttle body 108 to the sleeve 110 and collar 198 assemblyand, thus, to the intake pipe 188. Desirably, a washer 206 is positionedbetween the bolt 204 and throttle body 108. Advantageously, theinsulating sleeve 110 inhibits vibration and/or heat from beingtransferred from the engine 12 to the throttle body 108.

[0081] An insulating ring 208 is positioned between both the throttlebody 108, collar 198, and the air intake box 86. The insulating ring 208operates to inhibit engine vibration and/or heat from being transferredto the throttle body 108 through the air intake box 86.

[0082] The above-described induction system arrangement inhibitsvibration and/or heat produced by the engine 12 from being transferredto the throttle bodies 108, either directly through the engine 12 orindirectly through the stays 94 and air intake box 86. Such aconstruction is particularly advantageous due to the fuel injectors 132being connected to the throttle bodies 108. The fuel injectors 132contain electronic components that may be sensitive to vibration andheat. Insulating engine-produced vibration and heat from reaching thefuel injectors 132 increases their performance and operating life whilereducing the likelihood of premature failure.

[0083] Of course, the foregoing description is that of a preferredembodiment of the present invention, and various changes andmodifications may be made without departing from the spirit and scope ofthe invention, as defined by the appended claims.

What is claimed is:
 1. A watercraft comprising a hull defining an enginecompartment, an internal combustion engine disposed in the enginecompartment, the engine including an engine body defining a combustionchamber, an air induction system comprising an intake air chamberconfigured to guide air toward the combustion chamber, an electricalcomponent disposed within the air chamber, and an insulating membersupporting the air chamber relative to the engine body.
 2. Thewatercraft according to claim 1, wherein the electrical component is afuel injector.
 3. The watercraft according to claim 1 additionallycomprising a throttle body connected to the air chamber, the engine bodyincluding at least one intake port, the insulating member comprising anelastic member connecting the throttle body to the intake port.
 4. Thewatercraft of claim 3, additionally comprising an intake runnerextending from the intake port toward the throttle body, the elasticmember connecting the intake runner to the throttle body.
 5. Thewatercraft of claim 1 additionally comprising a throttle body having anoutlet end, a collar connected to the outlet end of the throttle body,wherein the insulating member comprises an inlet end configured toengage the collar.
 6. The watercraft according to claim 5, when thethrottle body is connected to the air chamber, the insulating membercomprising an elastic member having an inlet end configured to engagethe collar sufficiently to support at least part of the air chamber. 7.The watercraft according to claim 5, wherein the inlet end of theinsulating member comprises an annularly shaped channel configured toextend along an inner surface of the collar and an outer surface of thecollar.
 8. The watercraft according to claim 1 additionally comprisingat least one stay extending from a portion of the engine body other thanthe intake port to the air chamber.
 9. The watercraft according to claim8 wherein the portion of the engine body comprises a cam chamber cover.10. The watercraft according to claim 1, wherein the insulating memberis elastic.
 11. A marine-duty engine including an engine body defining acombustion chamber, an air induction system configured to guide air intothe combustion chamber, the air induction system comprising an intakeair chamber configured to guide intake air toward the combustionchamber, an electrical component disposed within the air chamber, and aninsulating member connecting the air chamber with the engine body. 12.The engine according to claim 11, wherein the electrical component is afuel injector.
 13. The engine according to claim 11 additionallycomprising a throttle body connected to the air chamber, the engine bodyincluding at least one intake port, the insulating member comprising anelastic member connecting the throttle body to the intake port.
 14. Theengine of claim 13, additionally comprising an intake runner extendingfrom the intake port toward the throttle body, the elastic memberconnecting the intake runner to the throttle body.
 15. The engine ofclaim 11 additionally comprising a throttle body having an outlet end, acollar connected to the outlet end of the throttle body, wherein theinsulating member comprises an inlet end configured to engage thecollar.
 16. The engine according to claim 15, when the throttle body isconnected to the air chamber, the insulating member comprising anelastic member having an inlet end configured to engage the collarsufficiently to support at least part of the air chamber.
 17. The engineaccording to claim 15, wherein the inlet end of the insulating membercomprises an annularly shaped channel configured to extend along aninner surface of the collar and an outer surface of the collar.
 18. Theengine according to claim 11 additionally comprising at least one stayextending from a portion of the engine body other than the intake portto the air chamber.
 19. The engine according to claim 18 wherein theportion of the engine body comprises a cam chamber cover.
 20. The engineaccording to claim 11, wherein the insulating member is elastic.
 21. Awatercraft comprising a hull defining an engine compartment, an internalcombustion engine disposed in the engine compartment, the engineincluding an engine body defining a combustion chamber, an air inductionsystem configured to guide air into the combustion chamber, the airinduction system comprising an intake air chamber configured to guideintake air toward the combustion chamber, an electrical componentdisposed in the air chamber, and means for insulating the electricalcomponent from engine produced vibrations.
 22. The watercraft accordingto claim 21, wherein the electrical component is a fuel injector. 23.The watercraft according to claim 21 additionally comprising a throttlebody connected to the air chamber, the electrical component beingconnected to the throttle body.
 24. A small watercraft comprising a hulldefining an engine compartment, an internal combustion engine disposedin the engine compartment, the engine including an engine body defininga combustion chamber, an air induction system configured to guide airinto the combustion chamber, the air induction system comprising andintake air chamber configured to guide intake air toward the combustionchamber, an electrical component disposed in the air chamber, and meansfor insulating the electrical component from engine produced heat. 25.The watercraft according to claim 24, wherein the electrical componentis a fuel injector.
 26. The watercraft according to claim 24additionally comprising a throttle body connected to the air chamber,the electrical component being connected to the throttle body.